The unwitting host was Silicon Valley Land Surveying, a mapping and land-surveying company based in San Jose.
An employee who asked not to be identified said the company is investigating the incident, which saw its Web site crash on Wednesday under an enormous surge in traffic.
The hostage video shows a blindfolded U.S. contractor named Paul Johnson, taken in the Arabian Peninsula by a group identifying itself as al-Qaida. Johnson was working as a mechanic for Apache attack helicopters in Saudi Arabia when he was kidnapped last Saturday.
The captors have threatened to kill Johnson on Saturday unless Saudi authorities release al-Qaida fighters held captive in the nation's prisons.
German magazine Der Spiegel first identified Silicon Valley Land Surveying as the source of the video. According to the magazine, the company's Web site was hijacked and turned into a host for the hostage video.